Hi, I'd like to help you with your question.
It certainly is very difficult when you are acting as a single parent to so many kids. It leaves you to act as both mother and father. It can be extremely stressful and hard on your relationship when you do not see your husband that often as well.
Is there a way to have your husband look for another job? Or does he not want to? It sounds like from your description of the situation that he is not concerned with the amount of time he is away and this is the main problem between the two of you.
If he is unwilling to see this as an issue, it leaves you with two choices. You can either leave him and the marriage or you can stay and modify the situation so you can at least reduce your stress level and manage the work load.
If you choose to leave, be sure you see a counselor to work out your feelings and sort out your arrangements with someone who can offer objective insight and help you make the best choice possible for yourself.
If you want to stay, try talking with your husband again. Let him know that the stress is overwhelming for you and you'd like to help him find a better solution, such as a new job. You can offer to help out by finding a job for yourself so your husband could take a lower paying job and your salary could offset the difference.
If he refuses to work with you on fixing this situation, then you will need to find ways to cope with the work load of being a single parent. It may be a very good idea for you to find work yourself, just so you have an outlet and a way to have your own income. You can also see if there is anyone who can stay with your kids while you get away for a while. Go visit friends or family for a few days. Or just go on your own somewhere. The goal is to have time to reduce stress and feel more energized.
Have the kids pick up more of the work load at home as well. Assign chores that your husband would normally do if he were home. Have the kids help with laundry, make dinner, etc. These are excellent skills for them to learn anyway since they will soon leave your home and be on their own.
And consider seeing a counselor by yourself if your husband will not go. The therapist can do a full evaluation to determine if you have a diagnosis (probably one that is stress related) and what your treatment needs are. You may also want to have your medication reevaluated. Lithium is an extremely strong medication usually reserved for those who are diagnosed with Bipolar disorder. Talk with your doctor and your therapist about why you were prescribed this medication and if it is the correct medication for you. You can find a therapist by asking your doctor for a referral. You can also search on line at http://therapists.psychologytoday.com/rms/. Talking with your pastor is also an excellent idea and it is good you have already taken this step.
Here are some books that will help:
The Complete Single Mother: Reassuring Answers to Your Most Challenging Concerns by Andrea Engber and Leah Klungness (although you are not totally a single parent, you are very close to being one.)
The Relaxation & Stress Reduction Workbook (New Harbinger Self-Help Workbook) by XXXXX XXXXX, XXXXX Robbins Eshelman, Matthew McKay and Patrick Fanning
We Need to Talk Tough Conversations With Your Spouse: From Money to Infidelity Tackle Any Topic with Sensitivity and Smarts by XXXXX XXXXX
You can find these books on Amazon.com or your local library may have them for you.
I hope this has helped you,